In the production of adipic acid by the liquid phase nitric acid oxidation of cyclohexanol and/or cyclohexanone in the presence of a copper-vanadium catalyst there generally results a purge waste stream containing valuable copper and vanadium ions therein of which recovery is desired if the process is to operate economically. These purge waste streams are generally derived from the mother liquor of one or more crystallizations involved in the recovery of the adipic acid and the necessity for purging arises because of the buildup of other dibasic acids such as succinic acid and glutaric acid. It is obvious that in view of the value of such catalyst metals, recovery of them from the purge waste stream is desirable before discarding same.
The basic process for the nitric acid oxidation of cyclohexanol and/or cyclohexanone in the presence of a copper-vanadium catalyst is well known in the prior art. The feed mixture utilized in most industrial processes is a mixture of cyclohexanone and cyclohexanol derived from the air oxidation of cyclohexane although some processes utilize only cyclohexanol or only cyclohexanone as a feed to the nitric acid oxidation. The cyclohexanol and/or cyclohexane is generally mixed with from 5 to 40 times its weight of an aqueous nitric acid solution, the nitric acid solution being generally of a concentration of 35 to 65% by weight, and there is also added the metal catalyst. Usually the copper and vanadium are added as ammonium metavandate and copper turnings, the total amount of catalyst usually being about 0.05 to 1.0% by weight of the reaction mixture. The liquid phase nitric acid oxidation is generally conducted at temperatures within the range of about 55.degree.C to 100.degree.C pressures within the range of about 1 to 5 atmospheres absolute.
There is produced in the nitric acid oxidation a liquid reaction product comprising the adipic acid and which also contains succinic acid, glutaric acid, nitric acid, water and the copper and vanadium catalyst values. Adipic acid crystals are recovered from the liquid reaction product by crystallization techniques, there resulting a mother liquor which comprises an aqueous nitric acid solution containing copper and vanadium values as well as dibasic carboxylic acids (mainly glutaric and succinic acids although some unrecovered adipic acid may also be present). A portion of this mother liquor may be and is generally recycled to the nitric acid oxidation reactor although a portion must be removed or purged to prevent buildup of the succinic and glutaric acid impurities, the portion removed or purged being the above-mentioned purge waste streams. The recovery of the adipic acid by crystallization is well known and such may be accomplished by one or more crystallization stages and may include effecting a removal of some nitric acid and water and re-dilution between crystallization steps.
Various methods have been developed for recovery of the copper and vanadium values from these purge waste streams as may be seen from U.S. Pat. Nos. 3,106,450; 3,186,952; 3,463,740; and 3,554,692. Also see British Patent Specifications 980762 and 956403. Even though various means have been derived for treating these purge waste streams so as to recover the catalyst values and other valuable components thereof, since the economic practicality of a given process often depends on a relatively narrow margin, research is constantly under way for a new and useful process for accomplishing the desired results.
It is thus an object of the present invention to provide a new and useful method for treating the above-described purge waste streams derived from an adipic acid process so as to recover valuable components thereof. It is a particular object of the present invention to provide a process for treating such purge waste streams so as to recover the copper and vanadium values therein. Additional objects will become apparent from the following description of the present invention.